[neutron-mc] Neutron parameters and EXTEND
Emmanuel FARHI
farhi at ill.fr
Fri Mar 28 08:26:21 CET 2008
Hi Aaron,
you are right, the intersection test is with the whole cylinder, and so
does the SCATTERED flag. I may fix that today in the CVS
E.
> Hi Emmanuel,
>
> I used your suggestions; I hadn't realized that the x, y, z names referred
> to local coordinates, which is exactly what I needed.
>
> Still, for some reason I am getting many more printf neutron x,y,z
> parameters than are recorded in the detector. In a recent run I had 785
> printf parameters and "monitor_N=202" output on similation end. I'm not
> clear as to why this might be happening. It seems as though both
> conditions
> in the IF statement in the EXTEND of the detector should only allow printf
> for neutrons that are scattered and intersect the detector. On second
> thought, this might not be the case. I recall seeing "intersect" as a
> flag
> in the component definition for Monitor_nD. However, could it be possible
> that SCATTERED is allowing any rays that intersect the entire cylindrical
> shell of the detector (i.e. as if on theta: limits = [0, 360])? I changed
> the limits to [10, 170] to see if this would change the results. This
> worked! The number of neutrons intersected in the detector now matches
> the
> number give by the printf.
>
> So it appears that SCATTERED it TRUE when a neutron intersects any part of
> the cylinder and not just the part defined by limits on theta.
>
> As a side note, the gauge volume that I am seeing looks strange. However,
> it is arranged in such a way that might explain the problems I've been
> having with divergences from the PowderN component. I won't be entirely
> confident on this until we fix the above problem and see what the proper
> gauge volume is.
>
> Here are the source, sample and detector components:
>
> COMPONENT source = Virtual_input(
> file = file, type = "text", verbose = 0, repeat_count = repeat,
> smooth = 1)
> AT (0, 0, 0) RELATIVE origin
> EXTEND
> %{
> flag=0;
> %}
>
> COMPONENT sample = PowderN(
> reflections = "Ni.laz", format = Lazy, d_phi = 8,
> radius = 0.006, yheight = 0.06, pack = 1, sigma_abs = 0,
> sigma_inc = 0, Delta_d = 0, frac = 0, tfrac = 0, DW = 0,
> concentric = 0, barns = 1)
> AT (0, 0, 0) RELATIVE sample_arm
> EXTEND
> %{
> flag=0;
> if(SCATTERED)
> {
> xp = x;
> yp = y;
> zp = z;
> flag = 1;
> }
> %}
>
> COMPONENT monitor = Monitor_nD(
> yheight = 0.133, xwidth = 2.794,
> options = "banana, theta limits=[10, 170], bins = 32")
> AT (0, 0, 0) RELATIVE sample_arm
> ROTATED (0, 0, 0) RELATIVE origin
> EXTEND
> %{
> if(flag==1 && SCATTERED)
> {
> printf("%g,%g,%g\n", xp,yp,zp);
> }
> %}
>
>
> On Thu, Mar 27, 2008 at 5:00 PM, Emmanuel FARHI <farhi at ill.fr> wrote:
>
>> Hi Aaron,
>>
>> I can see a few comments to improve and understand the possible problems
>> you face.
>>
>> 1- to extract the neutron stte parameters, you can not indeed refer
>> explicitely to the 'x','y' and 'z' names as these are only defined in
>> the
>> TRACE of each component. However, they should also be defined in the
>> EXTEND, and they are already in the local component coordinate frame.
>>
>> 2- if you want to extract coordinates from e.g. POS_A_CURRENT_COMP
>> (which
>> is a Coord structure), use the coords_get function (see Appendix at the
>> end of the User Manual). the 'A' in the name indicates this is in the
>> absolute coordinate frame. Better use the 'R' label, POS_R_CURRENT_COMP.
>> The 'x' 'y' 'z' fields of the structure can not be accessed as the names
>> xyz are redefined to point to the real name of the neutron coordinate
>> which is e.g. 'mcnlx'.
>>
>> 3- I would rather write your code as follow.
>> At the source level (or virtual output), make an EXTEND that sets the
>> flag
>> to 0. Suppose you have first a neutron that interacts with the PowderN.
>> It
>> sets the flag. But now, let's say a second neutron misses the sample.
>> The
>> extend block is NOT evaluated as the component is skipped (e.g. no
>> intersection with volume), and the flag value is the one from the
>> previous
>> neutron. You use a wrong flag value if that neutron reaches the
>> detector!
>>
>> Source=blah( ... )
>> EXTEND %{
>> flag=0;
>> %}
>>
>> Then you can have you sample extension, and use directly the xyz values.
>> COMPONENT sample = PowderN( ... ) AT (0, 0, 0) RELATIVE sample_arm
>> EXTEND
>> %{
>> flag=0; // make sure we always define it when reaching sample
>> if(SCATTERED) {
>> xp = x; // local coords
>> yp = y;
>> zp = z;
>> flag = 1;
>> }
>> %}
>>
>> Try these modifications, and tell me. Using global variables in EXTEND
>> may
>> get tricky as you are not sure to pass there. So, better make sure you
>> control all variables, and this should be done at least at some position
>> were all neutrons pass. There is a similar difficulty with the SPLIT
>> keyword.
>>
>> Emmanuel.
>>
>>
>> > Hi all,
>> >
>> > I've been working on a way to essentially visualize the gauge volume
>> in
>> a
>> > sample. I'll give a brief summary of my instrument and then the
>> problems
>> > that I've found:
>> >
>> > It's a simple 2-axis instrument, with such components as: a
>> > Source_Maxwell_3, a Monochromator_flat, a PowderN and a Monitor_nD.
>> I've
>> > used a virtual_input/virtual_output to save neutron histories at the
>> > sample
>> > incident slit. I can then continue these histories through
>> diffraction
>> > from
>> > the sample and to the detector.
>> >
>> > In order to visualize the gauge volume, I thought I could do the
>> > following:
>> >
>> > 1) Use EXTEND and if(SCATTERED) in the sample component to save the x,
>> y,
>> > z
>> > position of the scattering event in the sample and also create a flag
>> if
>> > the
>> > neutron was scattered at the sample (example flag = 1 if SCATTERED,
>> ELSE
>> > flag = 0)
>> >
>> > 2) Use EXTEND and if(flag==1 && SCATTERED) at the detector. Then
>> printf
>> > the
>> > saved x, y, z positions of the scattering events in the sample from
>> above.
>> > (here I am using printf for debugging, eventually I would like to use
>> the
>> > DETECTOR OUT 3D(...) macro).
>> >
>> > The problems that I'm having:
>> >
>> > 1) I cannot seem to find a variable(s) that define the location of the
>> > scattering event in the PowderN component. I have been using simple
>> the
>> > global variables 'x' 'y' 'z', but I don't think this is working
>> correctly.
>> >
>> > 2) The printf is outputting many more neutron x,y,z than actually hit
>> the
>> > detector. My speculation is that the SCATTERED macro does not work in
>> > detectors?
>> >
>> > 3) A smaller problem. What I would like is the local x-y-z of the
>> > scattered
>> > neutron in the sample. To do this, I've tried using the
>> > POS_A_CURRENT_COMP,
>> > but I can't seem to isolate the x,y,z components of this vector. I've
>> > tried
>> > using POS_A_CURRENT_COMP.x to get the x-component, but this does not
>> seem
>> > to
>> > work as I get the following error:
>> >
>> > In function `mcraytrace':
>> > 87: error: structure has no member named `mcnlx'
>> >
>> > Here is a sample of the EXTEND sections. ** indicates a comment that
>> I've
>> > added for clarity:
>> >
>> > COMPONENT sample = PowderN(
>> > reflections = "Ni.laz", format = Lazy, d_phi = 8,
>> > radius = 0.006, yheight = 0.06, pack = 1, sigma_abs = 0,
>> > sigma_inc = 0, Delta_d = 0, frac = 0, tfrac = 0, DW = 0,
>> > concentric = 0, barns = 1)
>> > AT (0, 0, 0) RELATIVE sample_arm
>> > EXTEND
>> > %{
>> > if(SCATTERED)
>> > {
>> > **here I'm trying to get the location of the scattering event (using
>> the
>> > state parameters x, y, z) and then put that into the local coordinates
>> of
>> > the sample using the POS_A_CURRENT_COMP ***
>> > xp = x - POS_A_CURRENT_COMP.x;
>> > yp = y - POS_A_CURRENT_COMP.y;
>> > zp = z - POS_A_CURRENT_COMP.z;
>> >
>> > **the flag is later used in the detector to indicate that the neutron
>> was
>> > scattered from the sample**
>> > flag = 1;
>> > }
>> > else
>> > {
>> > flag = 0;
>> > }
>> > %}
>> >
>> > COMPONENT monitor = Monitor_nD(
>> > yheight = 0.133, xwidth = 2.794,
>> > options = "banana, theta limits=[88.75, 91.25], bins = 32")
>> > AT (0, 0, 0) RELATIVE sample_arm
>> > ROTATED (0, 0, 0) RELATIVE origin
>> > EXTEND
>> > %{
>> >
>> > **Here the xp, yp, zp from above should only be printed if the neutron
>> was
>> > scattered from the sample and intersected the detector
>> > if(flag==1 && SCATTERED)
>> > {
>> > printf("%g,%g,%g\n", xp,yp,zp);
>> > }
>> > %}
>> > --
>> > *************************************************
>> > Aaron M. Percival
>> > M.Sc. Candidate
>> > Dept. of Physics, Engineering Physics & Astronomy
>> > Queen's University
>> > Kingston, Ontario, Canada, K7L 3N6
>> > Office: 613-533-6000 ext. 74789
>> > Fax: 613-533-6463
>> > *************************************************
>> > _______________________________________________
>> > neutron-mc mailing list
>> > neutron-mc at risoe.dk
>> > http://mailman.risoe.dk/mailman/listinfo/neutron-mc
>> >
>>
>>
>> --
>> FARHI Emmanuel <farhi at ill.fr>
>> Groupe DS/CS, ILL4/156, Tel 04 76 20 71 35
>> ILL, Grenoble
>>
>> _______________________________________________
>> neutron-mc mailing list
>> neutron-mc at risoe.dk
>> http://mailman.risoe.dk/mailman/listinfo/neutron-mc
>>
>
>
>
> --
> *************************************************
> Aaron M. Percival
> M.Sc. Candidate
> Dept. of Physics, Engineering Physics & Astronomy
> Queen's University
> Kingston, Ontario, Canada, K7L 3N6
> Office: 613-533-6000 ext. 74789
> Fax: 613-533-6463
> *************************************************
> _______________________________________________
> neutron-mc mailing list
> neutron-mc at risoe.dk
> http://mailman.risoe.dk/mailman/listinfo/neutron-mc
>
--
FARHI Emmanuel <farhi at ill.fr>
Groupe DS/CS, ILL4/156, Tel 04 76 20 71 35
ILL, Grenoble
More information about the mcstas-users
mailing list